[clang] [Doc][HLSL] Add documentation for root signature. (PR #83933)

[Chris B via cfe-commits]

https://github.com/llvm-beanz requested changes to this pull request.

I think we need to break this PR up into different parts going to different places.

Documenting the RootSignature grammar and usage in the Clang docs makes sense.

I think documentation of the RootSignature binary format probably should live with the DirectX backend docs, since the code to generate the binary encoding should live in LLVM.

The last part of the document here about the implementation I think we should remove from this PR and bring that discussion over to https://github.com/microsoft/hlsl-specs. There are a lot of parts of the design that I'm not convinced are correct or lack appropriate detail for me to understand.

To @damyanp's point I think the discussion thread here has gotten long enough to be unwieldy. Rather than merging an incomplete document to Clang's docs, I think it would be better for us to iterate on the design outside the LLVM source tree and return to LLVM with a design we have a higher level of confidence in.

@python3kgae can you strip PR down to just the first parts that document Root Signatures and take the implementation discussion over to hlsl-specs?

https://github.com/llvm/llvm-project/pull/83933